1. Field of the Invention
The present invention relates generally to a passenger restraint unit for an automotive vehicle. More particularly, the invention is directed to a failure monitoring system for a passenger restraint unit such as an automotive airbag safety unit.
2. Description of the Prior Art
It is current practice to incorporate an airbag safety system into automotive vehicles for protecting a vehicle occupant from impact upon occurrence of an accidental collision. For assuring the air bag safety system operates properly, various failure monitoring systems for such as a collision detecting circuit have been proposed.
For example, a failure monitoring unit which includes a switch arranged in series with a collision detecting circuit is well known in the art. In this failure monitoring system, only immediately after a reset signal is provided in a reset circuit, or a power source is turned on, the switch is opened to inhibit the operation of the collision detecting circuit and the operational test is performed for monitoring a malfunction in the collision detecting circuit.
The above conventional failure monitoring system, however, encounters a drawback in that when the reset circuit breaks down or malfunctions due to noise input, the operational test may be performed regardless of the time the power source is turned on. This results in an airbag system being actuated unnecessarily.